get ready anyway

Train yourself physically to be ready for a third set. If you are it'll be easier to be positive building confidence to win either in 2 or 3 sets.
Learnt from kick boxing, I build my own confidence thinking the more it lasts on the field the better I'll be over my opponent.
Build your positive attitude to the end of the match, whatever happens, thinking you'll be better than the other psychological. To work on thawhen you train with a partner, you can start every game with one or two points at his/her advantage, so you have to catch up. Doing so you'll teach your mind being lead doens't mean you'll loose.
As soon as you're physically and psychologically ready for a 3rd set, you'll see you'll finish your match in 2 with not problem on your side (of course depends from your opponent too). But you'll manage all from your side to win.
I don't wish you good luck because it has nothing to do with how you finish but wish you to get tough enough and get enough confidence to enjoy the match...even with a 3rd set ! ;-P